1. Field of the Invention
The present invention relates to bone implants and preferably to dental implants. More particularly, the invention relates to a bone implant that can be positively inserted and secured into the bone, preferably a jaw bone, by retention means provided in an elongated body of the implant. Even more preferably, the invention concerns a dental implant comprising a body to be secured within the jaw bone of a patient for receiving, after securement of the body in the bone, a dental prosthesis.
While specific reference to dental applications of the present implant will be made in the present disclosure and drawings, the bone implant of the invention is not restricted to dentistry but it may be applied to any other field where a prosthesis, a fixation device such as nail, etc. is to be secured into a bone. In addition, the term "patient" is applicable either to animals or human beings.
2. Description of the Prior Art
Bone implants, particularly dental implants, are well known in the dentistry field, many of them comprising a hollow or solid body to be secured into a bore within the bone. The body is adapted to be inserted in the socket of a tooth which has just been extracted so as to take the place of the removed tooth. The body must be retained within the socket without bridging or any other support from the adjacent or proximal teeth in the denture, and a prosthetic piece is then affixed in the body. To get a firm retention within the bone many retention means are provided in the body, always taking into consideration the benefits of the bone growth around the body and retention means. Most of the dental implants have looked for taking advantage of the bone growth to enhance the retentive function of the body in the bone. However, these known implants suffer from serious drawbacks. First, they fail to get a permanent retention and second, they are difficult to introduce into the bone.
To facilitate introduction of the implant into the bone, V-shaped threads are provided in most of the prior art implants. Generally, a bore is first drilled in the bone, preferably with a diameter lesser than the external diameter of the threads, which threads are designed to be self-tapping. However, this kind of threads is not reliable to get a proper retention of the implant in the bone. Implants are subjected to stresses and vibrations that resulting in loosening of the implants due to the lack of a reliable retention within the bone. This is due to a vectorial and rotational stresses appearing during chewing, biting, etc. and V-shaped threads, instead of proving retention, promotes the bone wearing and cracking.
It is well known in the art that a V-shaped thread transmits a 10 times greater shear force than a square thread design ("Implant Design Considerations for the Posterior Regions of the Mouth", Implant Dentistry, Vol. 8, Number 4, 1999), however, V-shaped threads are desired for tapping the bone and square threads only provide retention in the longitudinal or axial sense but no lateral retention is provided.
To overcome the above drawbacks several attempts have been made. U.S. Pat. No. 3,579,831, to Stevens et al., discloses a dental implant comprising a partially solid body including an external screw and a plurality of pins transversely passing through the body and extending into the bone jaw to provide an stabilization and anchoring result. This structure, however, needs of several components and the bone may be weakened by the insertion of multiple parts into the same, which components, like the pins, may also cause damages to adjacent teeth roots.
U.S. Pat. No. 3,708,883 to Flander, discloses an expandable dental implant comprising a body with a bottom portion having extensions which are spreadable for pressing the same against the bone, at a bore previously made in the bone. An expanding piece having a threaded shank is located into the body and a nut is threadably arranged in the shank. The nut may be rotated to cause the shank to lift and the expanding piece to spread the extensions of the body. The extensions are provided with external V-shaped threads or projections.
U.S. Pat. No. 6,008,431 to Caldarise, et al. discloses a bone prosthesis having a surface topography with recesses including a growth enhancement coating at the bottom of the recesses. The recesses have a depth of under three millimeters so that new bone growth spans the recesses and penetrates into the prosthesis over an extended surface textured region. While the dove-tail shaped recesses are already well know to enhance a rigid attachment and retention, the textured surface of Caldarise et al. does not provide threads necessary for screwing the implant into a bore in a bone or even for self tapping the bone.
U.S. Pat. No. 6,042,380 to De Rowe discloses an expandable dental implant designed to be inflated and deformed once in bore bone the patient to enhance retention, the implant including a deformable spiral tube which is wrapped around a central pin. The attachment thus is being improved by the deformation and shape of the tube but no screwing capability is provided.
It would be therefore convenient to have a bone implant capable of being easily inserted into a bone, preferably into a bore in the bone, and capable of being firmly attached in the bone with a permanent integration of the implant in the bone structure.